1. Technical Field
The present invention relates to image preview in an image pickup apparatus such as a still picture camera or a video camera.
2. Description of the Related Art
To allow the user to center the image coming from the image sensor on a scene, image pickup apparatuses are equipped with an optical or electronic viewfinder. The present disclosure more particularly applies to image pickup apparatuses equipped with electronic viewfinders.
Electronic viewfinders comprise a display screen of relatively small dimensions and low resolution with respect to that of the apparatus image sensor. This display allows the user to view the image coming from the image sensor before saving an image or a sequence of images in full resolution, such as those provided by the image sensor.
To display an image coming from the image sensor on the viewfinder's display screen, the image is subjected to several processes in particular to adapt its resolution to that of the viewfinder's display screen. These processes often cause a reduction, even a suppression, of some defects of the image, like clarity defects and noise defects, which appear in particular in the presence of low lighting. These defects which are small or not visible on the viewfinder's display screen, become visible at printing or displaying an image saved at the resolution of the image sensor, for example on a display screen of bigger dimensions. Thus, the viewfinder of an image pickup apparatus does not always allow the defects of images to be viewed before saving, so that it is hard, and in some cases, even impossible for the user to adjust accurately enough some image pickup parameters like the image sensor sensitivity or the lens focus.
The user may admittedly make several attempts, each attempt consisting in saving an image and viewing a part of the saved image in zoom mode on the viewfinder screen. This method appears inappropriate to take a brief scene, and very tedious, in particular with some image pickup apparatuses comprising a complex control interface to allow numerous image pickup parameters to be adjusted. In addition, a correct adjustment of image pickup parameters often results from a tradeoff between several parameters. Furthermore, such an adjustment may be adapted to a situation, but disastrous in other situations. The user must therefore adjust these parameters to each scene.
Some image pickup apparatuses have a simplified control interface comprising several image pickup modes, each adapted to a particular situation, and each corresponding to a set of predefined setting values of the image pickup parameters. Some apparatuses also offer an automatic selection of an image pickup mode. However, these solutions cannot take into account all the possible image pickup situations.
Some more advanced apparatuses offer to automatically set all the adjustable image pickup parameters by performing an analysis of the image directly supplied by the image sensor. However, the setting algorithms used cannot be adapted to some types of scenes, and do not offer a setting as accurate as that resulting from user evaluation.